Microprocessor control of physical conditions is becoming more widespread as computerized systems are found to control functions with optimum efficiency. In a microprocessor-based solar controller (see in this connection "Microprocessor-Based Solar Controller" by Dave Corbin published in Radio Electronics, June 1978, at page 94, analog temperature information is converted into digital data through an analog-to-digital converter (ADC) to process information as efficiently and as accurately as possible. Other known microprocessor-controlled sensing devices make use of frequency oscillators with transducer dependent frequencies. The oscillator frequency is slow enough for the microprocessor to count cycles and, by doing so, determine from the timing the resistance of the transducer (e.g., thermistor). The resistance, in turn, determines the magnitude of the condition being sensed (e.g., temperature).
In contrast to the aforementioned condition sensors, the present invention measures conditions without the use of an external oscillator or ADC (analog-to-digital converter).